In dispensing molten metal through an orifice in a crucible for casting, especially continuous casting in a mold, it is desirable to constantly monitor and regulate the pressure in the melt in the crucible near the exit orifice. Conventional pressure transducers are unsuitable because of the high temperature in the melt.
Currently used systems for monitoring the conditions within a closed crucible and controlling the flow rate from the crucible generally employ two sensors: one for measuring the gas pressure above the level of molten signal; and one for measuring the level of the molten metal. Such systems may also include a source of super-atmospheric pressure gas alone or in conjunction with a source of sub-atmospheric pressure gas (a vacuum); control circuitry which receives signals from the gas pressure sensor and the liquid level sensor; and valves controlled by the control circuitry for controlling the amounts of super-atmospheric pressure gas and sub-atmospheric pressure gas supplied to the crucible.
A representative example of a flow rate control system used with a bottom pour crucible is shown and described in U.S. Pat. No. 3,830,282 of Schultz. A representative example of a flow rate control system used with a top feed crucible is shown and described in U.S. Pat. No. 3,768,542 of Bosworth et al. Heretofore, insofar as I am aware, there has not been a successful system for monitoring the sum of both gas and liquid pressure in the crucible near the exit orifice to allow more efficient control of the molten metal flow.
It is, therefore, an object of the invention to provide a pressure transducer for monitoring the total pressure in the crucible, which can withstand the high temperatures of the molten metal, and which is capable of monitoring total presure at any desired location within the melt.
Another object of the invention is to provide a single pressure transducer which measures the sum of both the gas pressure and the pressure due to the molten metal in a crucible near the exit orifice.
Another object of the invention is to provide a processor for controlling the flow rate of molten metal from the exit orifice of a crucible by employing the steps of immersing a portion of a high temperature pressure transducer in the molten metal near the exit orifice of the crucible and measuring the total gas and liquid pressure exerted on a sensing surface of the immersed portion of the transducer.
It is an important principle in the art of precise measurement that the measuring instrument have structural characteristics which do not cause erroneous measurements. It is thus another object of the invention that the design of the pressure transducer be such that erroneous measurements are not caused by the transducer itself during operation.